Adolescence is a time period of significant neurodevelopment, and is also a time when psychopathology begins to emerge in a sex-specific fashion. It is essential for us to understand what factors influence typical brain development and vulnerability for psychopathology. To date, research on brain organization and structure have been primarily studied in the developmental context of age. Recent research, however, suggests that puberty may uniquely contribute to the timing of neuromaturation differently in girls and boys, and may potentially contribute to the development of mental health problems that materialize during adolescence. However, the conclusions from the majority of these studies are limited due to their cross-sectional study design. The goal of the current project is to more fully characterize the influence of pubertal maturation, as measured by physical and hormonal assessments, on brain and mental health behaviors in typically developing girls and boys. Utilizing two independent longitudinal design datasets, the proposed study will use a multimodal approach, including structural and functional magnetic resonance imaging (MRI) and diffusion tensor imaging, to quantify the contributions of pubertal maturation in predicting changes in neurodevelopment within the same adolescents over an average of 2 years. Furthermore, the current study will examine if pubertal-related changes are distinct or similar depending on sex, and using behavioral self-reports, determine if individual differences in rates of pubertal-related brain maturation influence internalizing and externalizing behavior in typically developing adolescents. By improving our understanding of what role puberty plays in neurodevelopment, these experiments act as a novel and necessary first step toward determining if puberty's impact on neurodevelopment may help to explain the emergence of psychopathology in a sex-specific manner during adolescence.